The present invention relates to speed changing machines and more particularly to a structure of a variable transmission device which can rapidly and strictly change the speed.
Typical variable transmission device adapts a frequency converter to change the speed. The frequency converter connects a lot of electrical circuit which makes the structure more complicated and often breakdown. If one discards the frequency converter and replaces with a mechanical structure, the variable transmission device will become more practical and reliable.
The present invention has a main object to provide a structure of a variable transmission device which can rapidly and accurately change the rotation speed of an output shaft without using a frequency converter and complicated electric circuit.
Another object of the present invention is to provide a structure of a variable transmission device which has both the functions of speed acceleration and speed changing so as to adapt to different type of machinery.
Accordingly, the structure of a variable transmission device of the present invention comprises generally an input. shaft driven by a motor to perform both positive and reverse rotations, an output shaft having gears at upper and lower ends for driving a working object to rotate and a speed changing shaft between the input shaft and the output shaft having gears at upper and lower ends meshed to the gears of the input shaft. The gears of the speed changing shaft are connected with bearings therebetween so that they can be rotated freely. Further, the speed changing shaft has a spiral outer periphery engaged with a inner threaded gear which is driven by a gear at the middle of the input shaft to rotatably slide in turn to the upper most position or the lower most position of the spiral outer periphery of the speed changing shaft. Because of that the input shaft rotates clockwise or counter clock wise over and over again, the inner threaded gear will repeatedly slide up and down. When the inner threaded gear reaches to the upper or lower gear of the speed changing shaft to closely engage with the upper or lower gears of the speed changing shaft the gears will be rotated at full speed as that of the input shaft. When the inner threaded gear leaves the upper or the lower gear of the speed changing shaft, it will slow down and gradually change the rotation direction. Therefore, the output shaft which is driven by the speed changing shaft is rotated at different speed ratio and different directions.